This invention is directed primarily to the corrugated board industry. Corrugated board is manufactured by first adhering a first flat liner to a median having a plurality of evenly spaced ridges (corrugations) thereon. This is accomplished by running the median through a corrugator which forms the ridges or corrugations. This first liner/median combination is then adhered to a second liner at a glue station. The two layers have adhesive applied therebetween.
The adhering layers then pass through a section of the assembly line where heat and pressure are applied to cause the layers to effectively adhere to one another. This section of the assembly line is often referred to as the "double facer" section. The double facer section of the assembly line includes a hot plate section and a cooling section. The hot plate section includes a means for applying pressure and heat to the adhering layers to accelerate the adhering process. In the hot plate section, the adhering layers pass below a pressure applicator and above a heat source.
The adhering layers then move into the cooling section which includes belts located both above and below the corrugated board. The belts contact the adhering layers and move it through the assembly line. The board cools as it moves through the cooling section. The adhesive between the layers cools as the board passes through the cooling section which completes the adhesion process. Once adhesion is effectively complete, the corrugated board is moved on through the assembly for cutting into various shapes for chests, cases, cartons and the like.
This invention has particular application to the hot plate section of the corrugated board manufacturing process. When the corrugated board passes through the hot plate section, the adhering layers pass over steam chests. The steam chests have steam supplied thereto by a boiler. The steam is cycled through the steam chests to heat the chests to an ideal temperature of approximately 355.degree. F. When the layers pass over the steam chests, the heat dries the board and the adhesive, which is typically a starch based adhesive.
In addition to heat, adhesion and board uniformity are accelerated by applying pressure to the adhering layers. In a typical corrugated board assembly plant, the adhering layers pass between the steam chests and a continuous belt, known as a corrugator belt. Corrugator belts are located in the hot plate section and the cooling section of the double facer. In the cooling section, the layers pass between two corrugator belts, which are compressed by a series of rigid weight rollers. The corrugator belts must contact the layers in order to move the layers through the assembly line.
In a typical hot plate section, the belt is compressed onto the board by a series of rigid roller bars rotatably mounted to a frame located proximate to the adhering layers of corrugated board. The roller bars contact a continuous belt, a corrugator belt which contacts the adhering layers. The pressure supplied by the roller bars serves to dry the corrugated board and the adhesive thus creating a bond between the layers. The removal of moisture from the corrugated board is critical to the control of warpage. This moisture is removed in the hot plate section by heat transfer from the contact with the steam chests. This contact must be throughout the entire surface of the board in order to control its quality. The moisture removal from the corrugated belt is also critical, since when the belt becomes saturated, moisture may then only escape the board at the edges. The lack of moisture removal creates warped board. The pressure in this section also serves to apply continuous contact to the belt and the adhering layers which pulls the corrugated board through the double facer. In the cooling section, which is the main pulling section for the board, the board is held between the same upper corrugator belt, and a lower corrugator belt instead of steam chests. These belts are typically kept in contact with the board by a series of rigid roller bars. The compression applied by the roller bars serves to increase the friction between the belts and board, which pulls the board through the double facer.
Turning now to the hot plate section of the corrugated assembly line, as the steam chests heat, they warp and deform. When the board passes over the hot plate section, it has been found that heat is only transferred at points of contact between the steam chests and corrugated board. The deflection of the steam chests cause gaps between the board and chests. These air gaps do not permit the board to dry, which creates warped corrugated board, which in turn wastes manufacturing and down time, and wastes materials. Thus, it is critical in the hot plate section that pressure is applied to the board over as much of the surface area as possible. In addition, because the rigid roller bars only apply pressure to the layers at a tangential point along the roller bar, the time and point of contact is minimal. A more effective method of applying pressure to the layers would be to increase the surface contact and the time in which the pressure is applied.
Corrugated manufacturers also experience occasional crushing of the corrugations or ridges or "flutes" of the board as it passes through the hot plate section. This problem occurs primarily when the adhering layers pass between the roller bars and warped areas of the steam chests. The problem of flute crush is particularly increased at the edges of the corrugated board. Where the moisture from the adhesion process lingers making the edges of the corrugated board the last to dry. Due to this lingering moisture, the edges of the board become especially susceptible to crush by the roller bars due to the high force generated by the tangential point on the roller bar and the weakness of the adhering layers due to the retained moisture. It would be advantageous to have a device and method that applied pressure in the double facer section of the corrugated manufacturing process evenly over a large number of flutes so that the problem of flute crush would be eliminated. It would also be advantageous to provide a device and method that effectively absorbs and dissipates the moisture in the adhesive of the adhering layers of corrugated board as the layers pass through the double facer section.
Because the roller bars pass over the layers for a short period of time, the number of steam chests and thus the length of the assembly line, must increase to insure that the adhesion between the layers is complete before the corrugated board is passed to the next section of the assembly line. Additional steam chests increase manufacturing time and cost due to the additional energy needed to operate the boilers which supply steam to the steam chests. In addition, the steam chests take up considerable space along the assembly line and increase the length of the assembly line. It would be advantageous to increase the contact between the adhering layers of the corrugated board and the steam box so as to create an effective adhesion in a shorter period of time. This would allow the corrugated board manufacturer to either decrease the length of the assembly line or increase the speed at which the corrugated board passes therethrough.
The present use of roller bars also causes problems when a foreign object, such as a large deposit of adhesive, moves between the layers and the belt. The roller bars cannot compensate for such a situation. This results in ripping of the belt or board, or jamming the feed of the board through the hot plate section. It would be desirable to have a means for applying pressure to adhering layers of corrugated board where the pressure applicator is retractable. This would allow the pressure applicator to retract when a foreign object passes underneath so as not to rip the belt or board or cause the board feed to jam.
The present use of roller bars also causes problems in the cooling section of the double facer. The cooling section is primarily responsible for pulling the corrugated board through the double facer section of the corrugated assembly line. In this section, the board is compressed between two corrugator belts as previously mentioned. The pressure is supplied by a series of roller bars rotatably mounted above and below the board and in contact with the corrugator belts. As discussed in detail above, this compression at the tangent points of the roller bars causes flute crush and increases the energy cost due to minimal contact with the frictional pulling forces from the belts compressed by the roller bars. It would be desirable to have a device and method of applying pressure to adhering layers of corrugated board as they pass through the cooling section of the double facer so that flute crush is eliminated and contact with the surface area of the adhering layers is increased so as to increase the rate at which heat and moisture dissipates from the board. An increase in contact between the pressure applicator and the surface area of the board would also decrease the energy needed to pull the board through the double facer. This would enable a plant to shorten the cooling section of the double facer and gain valuable manufacturing space and flexibility to run at higher speeds with an increase in energy savings.
Corrugator belts tend to be extremely expensive. A typical belt costs a manufacturer approximately $18,000. Thus, it is important for the manufacturer to maximize the belt life.
With regard to the present application, the weight of the roller bars against the belt tends to wear the belt and causes and unnecessary decrease in the belt life. This increases manufacturing costs and down time to replace the belt. It would be advantageous to provide a device and method that applies pressure to the belt and corrugated board where the friction therebetween is minimized so as to increase belt life and enable the manufacturer to increase the speed at which corrugated board is produced. The weight of the weight rollers on the belt also causes significant drag. This causes substantial belt wear and early replacement of the belt which increases the overall manufacturing cost.
In addition to the problems described above, the use of the presently existing rotatably mounted roller bars requires considerable alignment, such as the use of alignment bearings and pins. These components require continuous maintenance, repair and replacement. This increases the manufacturer's overhead costs as well as time in the maintenance and down time when the roller bars are removed and replaced on the assembly line. It would be advantageous to have a corrugated board assembly wherein the pressure applied to the adhering layers of the corrugated board in the hot plate section was not dependent upon a series of alignment bearings and pins.
The prior art has failed to address the problems discussed herein. One device has replaced the roller bars with a series of flat plates connected to a frame by means of mechanical springs. This increases the surface area and time of contact between the adhering layers and the steam chests. However, the constant pressure of the mechanical springs does not compensate for changes in the shape of the steam chests as they deform as a result of increased heat. In addition, the flat plates have smooth bottoms that are in constant contact with the belt throughout their surface areas. These plates have no way of dissipating the heat and moisture so that the adhesion process is accelerated.
Another device attempted to solve the heat deformation problem by substituting the alignment bearings of the roller bars with a pressurized air bladder. Under pressure the air bladder acts as a shock absorber and provides a cushion to compensate, in part, for the deformation of the steam chests. However, because the roller bars are rigid, the increase in surface area contact between the adhering layers and the steam chest is minimal.
This device also attempted to increase the surface contact between the pressure applicator and the steam chest by providing for a continuous belt of mail. The weight of the mail against the steam chests increases the pressure against the adhering layers of corrugated board. However, the drag coefficient of the mail against the felt belt is considerably higher than conventional roller bars. As a result, this device requires a significant increase in energy to move the belt and adhering layers of corrugated board through the assembly line. In addition, the friction between the mail and the belt significantly decreases the belt life which further increases the cost of manufacturing.
Thus, there is a need for a device that applies variable pressure to adhering layers of corrugated board as they pass over steam chests in a hot plate section of a corrugated board assembly line so as to compensate for the heat deformation of the steam chests.
There is a further need for a device that applies pressure over an increased surface area of adhering layers of corrugated board as they pass over the steam chests.
There is still a further need for a device that varies the pressure applied to adhering layers of corrugated board across the width of the board as it moves through a hot plate section.
There is yet a further need for a device that decreases the time required to effectively adhere layers of corrugated board together which thus enables a corrugated board manufacturer to decrease the size of the hot plate section of the corrugated board assembly line.
There is still a further need for a device that applies variable pressure to adhering layers of corrugated board to effectively adhere such layers so as to enable a corrugated board manufacturer to increase the speed at which the adhering layers of corrugated board are fed through the hot plate section of a corrugated manufacturing facility.
There is yet a further need for a device that supplies variable pressure to adhering layers of corrugated board and a moveable belt as they pass through the hot plate section of a corrugated board assembly line where the friction therebetween is decreased.
There is even yet a further need for a device that provides variable pressure to a moveable belt and adhering layers of corrugated board so as to increase the belt life.
There is yet a further need for a device that provides variable pressure to adhering layers of corrugated board without deforming the adhering layers.
There is a further need for a device that quickly and effectively dissipates moisture and heat from adhering layers of corrugated board so as to prevent flute crush and decrease manufacturing time.
There is also a need for a method of applying variable pressure to adhering layers of corrugated board as they pass over steam chests in a hot plate section of a corrugated board assembly line so as to compensate for the heat deformation of the steam chests.
There is a further need for a method of applying pressure over an increased surface area of the adhering layers of corrugated board as they pass over the steam chests.
There is still a further need for a method of varying pressure applied to adhering layers of corrugated board across the width of the board as it moves through the hot plate section.
There is yet a further need for a method of applying variable pressure to adhering layers of corrugated board so as to decrease the time required to effectively adhere layers of corrugated board together and thus enable the manufacturer to decrease the size of the hot plate section of the corrugated board assembly line.
There is still a further need for a method of applying variable pressure to adhering layers of corrugated board that enables a corrugated board manufacturer to increase the speed at which the adhering layers of corrugated board are fed through the hot plate section as a result of more effective adhesion techniques.
There is yet a further need for a method of applying variable pressure to adhering layers of corrugated board and a belt so as to decrease the friction therebetween.
There is even yet a further need for a method for applying variable pressure to adhering layers of corrugated board so that the belt life is increased.
There is yet a further need for a method for applying variable pressure to adhering layers of corrugated board without deforming the adhering layers.
There is a further need for a method for applying variable pressure to adhering layers of corrugated board so that heat and moisture are quickly and effectively dissipated, flute crush is prevented and manufacturing time is decreased.